Solitary plasmacytomas are uncommon plasma cell disorders, which may present as a single bone lesion (P-bone) or extramedullary plasmacytoma (P-EM). There is a paucity of large studies analyzing prognostic factors and outcomes of plasmacytomas. While the treatment of choice is radiation therapy (RT), there is a lack of data evaluating optimal RT dose. In this study, we sought to answer these questions by utilizing the National Cancer Database plasmacytoma data from 2000 to 2011. A total of 5056 patients were included in the study (median age 62 years; range 52-72). To obtain a pure plasmacytoma cohort, potential multiple myeloma patients were excluded from the study (bone marrow involvement, systemic chemotherapy use). P-bone constituted 70% of the patients. The median overall survival (OS) of P-EM was significantly longer than P-bone (132 vs. 85 months), and for soft/connective tissue it was worse than remainder of P-EM (82 vs. 148 months). On multivariable analysis, factors associated with worse OS included older age (≥65), presence of P-bone, and treatment with a radiation dose <40 Gy.